The present invention relates generally to an electrical bridge attached to a high current switch, and more particularly to such a switch used in electrolysis systems including a plurality of electrolytic cells connected in electrical series circuits.
Such switches are used for separating an individual electrolytic cell, e.g. for the manufacture of magnesium, aluminum, etc., from its series circuit for periodic maintenance purposes, without interrupting current flow through the remainder of the cells in the circuit.
There are often more than one hundred cells in the series circuit, and usually the current carrying path goes through a bus-bar from the cathode of one cell to the anode of the next cell. Disconnection of a cell is achieved in practice through the use of one or more "shunting" or "bypass" bars which are connected parallel to the cell so that the current bypasses the actual cell.
The extremely high currents involved, e.g. up to 200,000 amperes encountered in the operating of modern cells and up to 250-300,000 amperes on projected cells of the future, result in severe arcing at the contact surfaces of the bypass bars and the bus-bars during the operations of opening and closing the switch. This presents a safety hazard for the operating personnel and also results in the erosion of the contact surfaces, thereby causing high maintenance costs.
This problem has been met in practice through the reduction of the current in the entire series circuit, or often through completely switching off the current during the engagement of bypass bars. This however is an expensive practice, not only because of the production losses throughout the entire circuit of cells, but additionally since later on there might arise serious irregularities in cell operation due to the reduction or switching off of the current. In recent years several types of high current switches have therefore been developed and put into use. Different models have been presented, the constructions being adapted to complicated bus-bar systems, which are designed e.g. for modern electrolytic series for the production of aluminum, in order to suppress or compensate for detrimental electromagnetic forces. Fast operating switches, designed to withstand the high currents occurring during the short periods of time when the bypass bars are connected to or disconnected from the bus-bars, are the features commonly employed in these prior art switches. However, in spite of the fact that such switches function satisfactorily with regard to personnel safety and production losses, these switches do not solve the serious problem of arcing on the contact surfaces.
U.S. Pat. No. 3,542,987 describes the use of a pair of resiliently mounted secondary contacts which are adapted to protect the main contacts against arcing damage. Such switches are used on electrolysis cells for the electrolysis of water solutions, e.g. for chlorine electrolysis. The switch consists of an adequate number of contact units so that the current load amounts to only a few thousand amperes per contact. One contact in every contact unit is arranged as a secondary contact designed as a resiliently mounted contact arm adapted to engage prior to engagement of the main contacts when the switch is being closed, and to part subsequent to the parting of the main contacts when the switch is being opened. All the contacts are moved through a common eccentric rotary shaft. The construction is complicated and, because of all of the movable and rotating parts, is unsuitable for use in the dusty atmosphere which is typical of a conventional electrolysis hall or system during the electrolysis of melted salts.